Natural Killer T (NKT) cells are a distinct subset of T cells with the unique capacity to produce a vast array of cytokines upon activation. NKT cells play a crucial role in regulating immune responses in a variety of settings, including infectious diseases, autoimmunity, and tumor immunity. However, little is known about the requirements for the development of NKT cells. To further elucidate the cellular requirements for NKT cell development, a new transgenic mouse model in which only T cells express CD1d (Lck-CD1d transgenic mice) was generated. This model system will be used to determine the effects of T cell-specific CD1d expression on NKT cell development and function. Preliminary studies indicate that T-cell specific expression of CD1d is sufficient to mediate the development of NKT cells. A better understanding of NKT cell development may lead to new strategies to manipulate their function in vaccination and immunotherapy protocols. [unreadable] [unreadable]